Low Cyanuric Acid

Cyanuric Acid Low In My Pool - How To Increase It?

Cyanuric acid is a vital component of swimming pool chemistry, but many people are unaware of its function and importance. Cyanuric acid (also known as CYA) is necessary in a pool because it acts to maintain consistent levels of chlorine, and it is especially needed in outdoor pools.

In this article, we will teach you everything you need to know about cyanuric acid in order to keep your pool’s chemistry balanced. We will cover ways you can identify low cyanuric acid, the causes of low cyanuric acid levels, and two reliable methods you can use to raise and maintain the cyanuric acid levels in your pool.

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How to Identify Low Cyanuric Acid Levels

One sign that you may have low levels of cyanuric acid in your pool is if you have a hard time maintaining adequate levels of chlorine. Although chlorine imbalance can also be a sign of other issues, it is often a sign of low cyanuric acid in your pool, which can allow chlorine to degrade faster over time.

The only effective way to determine low cyanuric acid in your pool is by using a test-kit designed for this purpose. We recommend a cyanuric acid test kit as opposed to test strips, because liquid test kits provide more accurate results and can detect a wider range of levels.

This test kit comes with easy to follow instructions and is able to detect a full range of cyanuric acid levels. This makes it an ideal kit to use when making adjustments to your pool’s chemistry that may affect the acid levels.

When correcting low cya, it’s important to avoid increasing the level too much, as high cyanuric acid can lead to other problems with pool chemistry.

What Causes Low Cyanuric Acid?

There are a couple main causes of low cyanuric acid in your pool. The most common cause is the use of unstabilized chlorine.

You may be using unstabilized chlorine regularly, which is not recommended for outdoor pools, or you may have introduced unstable chlorine to your pool as part of a shock treatment, which can drastically lower the amount of free cyanuric acid molecules.

When added to your pool water, unstabilized chlorine transforms into sodium hypochlorite ions. These are brittle chlorine molecules that have a tendency to degrade quickly in sunlight. Unstabilized chlorine will bind to any free cyanuric acid in your pool in order to make the sodium hypochlorite ion more stable, but this process uses up any available cyanuric acid.

Unstabilized chlorine is commonly sold as liquid chlorine, lithium hypochlorite, calcium hypochlorite, or salt-generated chlorine. Check your chlorine package to see if your product has a chlorine compound that does not contain cyanuric acid.

Another cause of low cyanuric acid is refilling your pool. Adding fresh water to your pool, whether it’s through rainfall or topping off your water level after a swimming event, introducing new water can lower the cyanuric acid level in your pool. This effect can occur even if you are using stable chlorine, depending on how much fresh water was added to the pool.

Expect low CYA levels after a heavy storm.

Why Low Cyanuric Acid is Bad for Your Pool

Low cyanuric acid levels are bad for your pool because it allows brittle, unstable chlorine to degrade faster in the sunlight. In order to maintain an appropriate chlorine level in your pool without adequate cyanuric acid, you would have to purchase much more chlorine than you would normally need.

Consequently, it’s much harder to maintain appropriate chlorine levels, and you may find yourself more vulnerable to algae blooms.

Cyanuric acid works by stabilising pool chlorine, which protects chlorine from sunlight, but can also prevent your chlorine from binding to other free chemicals in your pool. This can cause unstable chlorine to produce higher amounts of wear on pool equipment over time, especially parts made out of plastic.

Free chlorine can also bind to ammonia based pool contaminants, such as certain types of sunscreen, or urine. When free chlorine binds to an ammonia base, it produces a very strong chlorine smell which may linger on swimmers hours after they’ve exited the water.

How to Raise the Cyanuric Acid Level in Your Pool

If you have low cyanuric acid levels, there are two main ways you can raise the levels to normal amounts: by adding cyanuric acid directly, or by switching to a stable form of chlorine. Luckily, both options provide an easy way to increase cyanuric acid in your pool.

Adding Cyanuric Acid

Adding cyanuric acid directly is our recommended option, as it allows you to control the stabiliser concentration independently of the chlorine concentration. It can also make a great first step in adjusting back to normal levels before switching to a stabilised form of chlorine. This will reduce the amount of stable chlorine you need to add to your pool.

Cyanuric acid is often sold under the name ‘pool stabiliser’. Liquid stabiliser is popular because it requires no mixing. 2.5L of these liquid products usually raises the cyanuric acid levels in a 25,000L pool to 32ppm, which is high enough to prevent chlorine degradation.

If you have an exceptionally large pool, a bigger powdered pool stabiliser may be a more cost-effective choice for you. This stabiliser is added to your skimmer box while you have your filter running.

1kg of powdered pool stabiliser is enough to raise your cyanuric acid levels to 50ppm (in a 20,000L pool). This is slightly on the high end of the acceptable range for cyanuric acid levels, which officially falls between 30-50ppm, so you may need to adjust your dose.

Use this pool stabiliser calculator to work out the appropriate dose for your pool. Make sure that you don't add too much, otherwise you will end up with high cyanuric acid levels, which can bring its own problems.

Using Stable Chlorine

If you have chronically low cyanuric acid and your free chlorine levels are fine, it is better to add cyanuric acid stabiliser directly to your pool instead of using stabilised chlorine. This will stabilise any existing free chlorine in your pool, in turn reducing the chances of over-chlorination when you add new, stable chlorine.

However, if you do wish to use stabilised chlorine, it comes in two main forms, sodium dichlor and sodium trichlor. Sodium dichlor has a pH of 6.5, and is typically recommended for hot tubs because it is more durable in heated water. Most outdoor pools use sodium trichlor, which has a pH of around 3 and is commonly sold as ‘stabilised chlorine’.

All-in-one trichlor pool tablets are pretty good, because they allow for slow release. This makes them ideal for those seeking less maintenance, or for those leaving town on a holiday.

These tablets are placed in your pool’s skimmer basket or in a floating chlorinator to maintain adequate chlorine levels for up to a full week.

While long-term use of stabilised chlorine may seem attractive as you are essentially 'killing two birds with one stone', it is very easy to overdose the CYA beyond the recommended levels by doing this.

If your CYA gets too high, it will actually bind up too much of your chlorine, making it ineffective and creating an unsanitary and unsafe environment in your pool. For this reason, it's generally best to stick to using stabiliser + unstabilised chlorine separately.


Cyanuric acid is essential to maintaining adequate pool chemistry because it acts as a chlorine stabiliser. Stable chlorine is a strong molecule that is less likely to break down in sunlight than unstable chlorine. Keeping adequate cyanuric acid levels ensure that you are getting the most effectiveness out of your chlorine product, and can prevent you from having to buy as much.

Do you have any remaining questions about cyanuric acid levels and how they can affect the chemistry of your pool? Be sure to leave a comment down below, one of our pool-care specialists will be happy to assist you!

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.